Tomas Berdych, who defeated US Open champion Marin Cilic 6-3, 6-1, could qualify for the last four with a victory over defending champion Novak Djokovic in his final Group A tie.

Tomas Berdych thrashed US Open champion Marin Cilic 6-3, 6-1 on Wednesday to remain in the hunt for a place in the semi-finals of the ATP Tour Finals.

Czech world number seven Berdych had been routed by Stan Wawrinka in his opening match at London's O2 Arena, but he bounced back in style and could qualify for the last four with a victory over defending champion Novak Djokovic in his final Group A tie on Friday.

"I think today was more about fighting and getting through it," Berdych said.

"It's not my first year. I have the experience of losing the first match in the past and I know how to come back. I think that was the biggest difference."

Quizzed during an on-court interview about the daunting task of facing world number one Djokovic, Berdych jokingly asked the crowd: "Any tips? I will need some.

"I just want to try to bring my best tennis and we'll see what happens. I hope I can have a great match."

Cilic's second straight-sets defeat at the season-ending event means the Croatian has no chance of qualifying after winning just six games in his two matches.

The 26-year-old made a whopping 30 unforced errors over the course of a woeful 74-minute meltdown.

"It's disappointing to play like this. I was not expecting it. But my body feels a little bit tired on the court," Cilic said.

"Especially with these guys at this kind of level, even small mistakes, or if you're not at your best, the outcome is not going to be going in your favour."

Berdych has lost his opening match of the Tour Finals in all five of his appearances, but the former Wimbledon runner-up had also won the next tie on each previous occasion and once again showed he could respond well to adversity.

Cilic, making his Tour Finals debut, had enjoyed important Grand Slam victories over Berdych at Wimbledon and then the US Open this year.

But Berdych got a measure of revenge for those losses with a dominant display.

After winning a combined four games between them in dismal opening match defeats, both players needed a fast start, and it was Berdych who seized the initiative as he broke in the first game.

Berdych had the momentum and even when Cilic earned two break points in the eighth game, the Czech was able to scramble out of trouble.

He sealed the opening set with another break and used his booming serve to escape when Cilic brought up two more break points early in the second set.

Cilic's shoulders slumped after that failure and the Croatian looked a spent force when he tamely directed a forehand wide to gift Berdych a 3-1 lead which effectively ended the one-sided contest.